The overall objectives of this research proposal are to 1) improve the understanding of the mechanisms that regulate the cerebral circulation in newborn infants; and, 2) to determine the importance of abnormalities in cerebrovascular control in the pathogenesis of brain injury in newborn infants. The specific aims are to use positron emission tomography (PET) for the measurement of regional cerebral blood flow, cerebral blood volume, cerebral oxygen extraction, and cerebral oxygen metabolism in preterm and term infants who have sustained brain injury or who are at risk for developing brain injury. These PET physiologic measurements will be correlated with: 1) neurological outcome; 2) systemic factors: cerebral perfusion pressure, arterial carbon dioxide tension, aNd arterial oxygen content; and, 3) the development of parenchymal infarction in preterm infants with intraventricular hemorrhage. The study of neurological outcome will be directed toward elucidation of the minimal value of cerebral oxygen metabolism that is associated with normal neurological development and, by extension, brain viability. The study of the systemic factors that affect the cerebral circulation and metabolism will be directed toward elucidation of the adequacy of the cerebral compensatory mechanisms to these factors. The study of the pathogenesis of periventricular parenchymal infarction in preterm infants will be directed toward identifying focal hemodynamic abnormalities in the periventricular white matter in infants with germinal matrix hemorrhage or intraventricular hemorrhage prior to the development of the infarct.